This invention relates in general to apparatus including devices and circuits therefor for sensing radiation and developing electrical signals in accordance therewith. The present invention relates in particular to such apparatus which senses and stores charge produced by electromagnetic radiation flux and which provides an electrical readout of the stored charge.
This application relates to improvements in the apparatus of copending patent application Ser. No. 441,054, now U.S. Pat. No. 3,890,500, filed Feb. 11, 1974, in the name of Eichelberger et al. and assigned to the assignee of this invention. The Eichelberger et al. application is hereby incorporated herein by reference.
The Eichelberger application Ser. No. 441,054, now U.S. Pat. No. 3,890,500, discloses a two-dimensional array of radiation sensing sites each comprised of a pair of coupled MIS (metal-insulator-semiconductor) capacitive cells. One cell of each cell pair is arranged to form the rows of array and the other cell of each cell pair is arranged to form the columns of the array. Readout of a row of sensing sites of the array is performed by a scanning technique of reducing the voltage on the row conductor line to cause the charge stored in the row oriented cells to flow to the column oriented cell coupled respectively thereto and thereafter, in turn, reducing the voltage on the column conductor lines to inject the stored charge into the substrate. This causes a current to flow in each column line. The column conductor lines are arranged in a plurality of consecutively numbered sets, each set including the same number of consecutively numbered column lines. Each of a plurality of charge integrating means are connected between a respective column line of a set and ground for simultaneous readout of the current flowing through the column lines of a set. A video channel circuit is associated with each of the integrating means for processing the signal from each set. The video signals from each video channel may be multiplexed to obtain a composite video signal.
It has been discovered when using the aforementioned readout techniques in which multiple readout circuits, each comprising a charge integrating means and a video channel circuit, that it is difficult to match the electrical characteristics of the circuit components of the readout circuits. When unmatched, a D.C. error or offset voltage is introduced into the composite video signal. This causes a display of a video frame of information to have columns of alternating intensity.
It is an object of this invention to provide improved surface charge storage devices and methods of operating such devices.
Another object of this invention is to provide arrays of sensing elements and readout circuits therefor of the kind described above in which a plurality of sensing sites may be simultaneously addressed for readout and the composite video signal generated thereby is substantially free of D.C. error voltages associated with such readout circuits.